Latent prints are invisible fingerprint impressions left on solid surfaces following surface contact caused by the perspiration on the ridges of an individual's skin on their fingers coming in contact with a surface and leaving perspiration behind, making an impression on it. Such fingerprint impressions may include substances like water, salt, amino acids, oils and also grime and various substances a person may have on their fingertip(s) or that may be present on a surface and able to accept an impression.
Conventional methods for extracting fingerprints usually involve adding chemicals or powders to the print. Such conventional methods can present an immediate dilemma in that they force the investigator to make a decision as to whether to dust for prints versus swabbing for DNA or chemical evidence present in the makeup of the print. Furthermore, such conventional methods are time-consuming and inconsistent, requiring some amount of trial-and-error on the part of an investigator before finding technique suitable for a particular fingerprint composition and fingerprint-bearing surface combination.
Automatic non-contact latent fingerprint detection systems are also known that avoid the need to add chemicals or powders that can disturb the surface chemicals of the fingerprint. Such systems generally include a single light source, which illuminates the surface with the latent fingerprint. However, these systems use light having a wavelength which does not optimize the contrast of the fingerprint image, among other disadvantages.